Coaxial communication active tap device and distribution system

ABSTRACT

An apparatus, system, and method for affordably distributing cable communication signals at greatly reduced power consumption levels with high signal quality with an active tap having gain stage characterized by low power (less than 1 Watt), low noise figure (less than 3 dB), high bandwidth (typically 2 GHz), and high gain (at least 15 dBmV).

BACKGROUND OF THE INVENTION

1. Field of Invention

A low-cost active tap for use in cable communication distributionsystems and characterized by low power consumption, low signaldistortion, and increased reliability.

2. Summary of the Background

In conventional coaxial communication distribution systems, signals aredistributed along cable lines. Consumers located along the length of thecable run are supplied with signals via passive taps. FIG. 1 is a blockdiagram of a conventional four-port 24 dB passive tap device. The inputsignal flows in parallel to a power-passing choke PPC1 and to a seriescircuit comprising a first capacitor C1, a directional coupler DC, and asecond capacitor C2. The directional coupler DC also outputs signals toa first splitter S1. This first splitter S1 feeds the signal then to apair of second splitters S2A and S2B. The output of the second splittersS2A and S2B then flows to output ports O1, O2, O3, and O4. Signals mayalso flow upstream from output ports O1, O2, O3, and O4, throughsplitters S2A, S2B and S1 and directional coupler DC to a node upstreamfrom the tap.

Because the components of the conventional tap are passive, theconventional tap attenuates the signal between its through-leg input andoutput as well as between its input and output to the subscribers. Thus,signal strength at the output of the device (e.g., 40.5 dBmV) is lowerthan at the input (e.g., 42.5 dBmV). The signal level at the outputterminal of the directional coupler DC feeding S1 is predetermined bythe design of the directional coupler. That is, a conventional DC16-typedirectional coupler provides a signal approximately 16 dB lower than theinput signal level (i.e., 26 dBmV).

In order to maintain consumer cable TV and other communication signalquality, components of the conventional passive tap device are typicallyselected depending on the tap input signal level so that the signallevel at each of output ports O1, O2, O3, and O4 is a minimum of 18 dBmVat the uppermost frequency. For example, as shown in FIG. 1, if theconventional passive tap device has an input of 42 dBmV, the directionalcoupler (DC-16) is selected to provide 26 dBmV at the input to splitterS1. This supplies 22 dBmV to S2A and S2B, which in turn supplies 18 dBmVto O1, O2, O3 and O4. This configuration also results in an output ofthe conventional tap device of 40.5 dBmV. As the signal level into thedevice decreases, the value of the DC also decreases and the throughloss of the device increases.

FIG. 2 shows an idealized model of a conventional system fordistributing signal from a source I1 to a number of consumers.Components of the conventional system include a source I1 in series withconventional passive taps P1-P18 and active line extenders LE1, LE2, andLE3. The passive taps P1-P18 each correspond to the device of FIG. 1,with the exception that the proper DC was selected to provide a minimumsubscriber output of +18 dBmV. With this configuration, 18 passive tapswith 4 output ports allow for 72 consumers to be supplied by source I1.

In FIG. 2 the figures of merit are composite triple beat (CTB);composite second order beat (CSO); and carrier-to-noise ratio (CNR). InFIG. 2, source I1 outputs a signal according the following profile: 54dBmV at 862 MHz, 48 dBmV at 550 MHz, and 39 dBmV at 55 MHz. In addition,the signal output from source I1 has a CTB of −64.0 dB; a CSO of −60.0dB; and a CNR of 51.0 dB. The signal propagates through the first fivepassive taps P1-P5 and coax during which the signals are attenuated to alevel where no more subscribers can be supplied with +18 dBmV. So thesignals must be amplified. The signals from the output of P5 arepresented at the input to extender LE1. Line extender LE1 is configuredto boost the signal to 49.5 dBmV at 862 MHz, 44 dBmV at 550 MHz, and 35dBmV at 55 MHz. The signal passes through the next four passive taps toline extender LE2. Line extender LE2 is also configured to boost aninput signal to 49.5 dBmV at 862 MHz, 44 dBmV at 550 MHz, and 35 dBmV at55 MHz. The signal passes through the next four passive taps to lineextender LE3. Line extender LE3 is also configured to boost an inputsignal to 49.5 dBmV at 862 MHz, 44 dBmV at 550 MHz, and 35 dBmV at 55MHz. The signal then passes through the final five passive taps. For thereasons noted relative to FIG. 1, the system is designed so that thesignal level at output ports O1, O2, O3, and O4 of each passive tap ison the order of 18 dBmV.

Throughout the propagation of the signal through the system, signal lossis introduced by the cable and passive taps. Line extenders are used toovercome the system losses but cause distortion to be added to thesignals. Thus, at the output of line extender LE1, CTB equals −60.5 dB;CSO equals −59.0 dB; and CNR equals 50.4 dB. At the output of lineextender LE2, CTB equals −58.0 dB; CSO equals −58.2 dB; and CNR equals49.8 dB. At line extender LE3, CTB equals −56.0 dB; CSO equals 57.5 dB;and CNR equals 49.3 dB. Since all the devices after each LE are passive,the distortion numbers are the same for all taps after each LE, untilthe next LE. For example, the last 5 taps all have a CTB of −56.0 dB.The previous 4 taps have a CTB of −58.0 dB. CTB adds on a 20 log basiswith the sum of the distortion of the source output plus the distortiongenerated by each LE. CSO and CNR add on a 10 log basis.

FIG. 3 illustrates signal characteristics for a more realistic cabletelevision signal distribution system developed with conventional systemmodeling software. In FIG. 3, source N1 outputs a signal onto a firstcable C1 of length 271 feet. The signal drops in strength due to linelosses and is split by splitter S1 onto cables C2, C3, and C6. Cable C2ends after 59 feet at a DC10 passive tap P1. Cable C3 extends 84 feet toa DC12 passive tap P2 which is connected to DC12 passive tap P3 via 230feet of cable C4 ₂. Passive tap P3 is connected to a terminating passivetap P4. Cable C6 extends 538 feet to line extender LE1 which connects toa DC16 passive tap P5 via an additional 268 feet of cable C7 (the totallength of cables C6 and C7 is 806 feet). Passive tap P5 connects to aDC8 directional coupler DC1 which is connected to a DC14 passive tap P6(on the down-leg) and to cable C8, which extends 259 feet to a DC12passive tap P7. Passive tap P7 connects to cable C9 which extends 277feet to in-line equalizer EQ1, which is connected to a DC4 passive tapP8.

Input and output signal levels (in terms of dBmV) at 862 MHz/750 MHz/55MHz, respectively, are shown in Table T1 TABLE T1 Device Input SignalLevel Output Signal Level N1 —/—/—   50/48/36.5 C1   50/48/36.546.5/44.7/35.6 S1 46.5/44.7/35.6 41.8/40.2/32.1 38.1/36.7/28.6 C238.1/36.7/28.6 37.3/35.6/28.4 P1 37.3/35.6/28.4   20/19/11 C341.8/40.2/32.1 40.7/39/31.8 P2 40.7/39/31.8   20/18/11 C4₂38.9/37.2/31.1 35.9/34.9/30.3 P3 35.9/34.9/30.3   20/18/14 C5₂34.1/32.8/29.7 25.5/24.8/27.5 EQ2 25.5/24.8/27.5 25.1/23.9/17.5 P425.1/23.9/17.5   17/15/12 C6 38.1/36.7/28.6 28.6/27.8/26.4 LE128.6/27.8/26.4   50/48/36.5 C7   50/48/36.5 46.5/44.7/35.6 P546.5/44.7/35.6   23/21/12 DC1 45.4/43.7/35.3 Through: 43.6/42.1/34.6Down-Leg: 37.4/35.7/27.3 P6 37.4/35.7/27.3   20/19/12 C8 43.6/42.1/34.640.3/39.2/33.7 P7 40.3/39.2/33.7   20/19/14 C9 38.5/37.1/33.134.9/34.4/32 EQ1 34.9/34.4/32 34.5/33.0/22.4 P8 34.5/33.0/22.4  17/16/11

FIG. 4 illustrates the power consumption of the idealized system of FIG.2. As shown in FIG. 4, power consumption of active line extenders LE1,LE2 and LE3 is 28.5 watts each, resulting in a total power consumptionof 85.5 watts. Based on a power supply located at the Source I1, and a0.500″ PIII DC loop resistance of 1.2 Ohms/1000 ft, the power dissipatedby the cable is 1.95 Watts. Power consumption of the conventional tapsis minimal because the only component that would dissipate any power inthe tap is the RF Choke (PPC1 in FIG. 1). The resistance of the RFChoke, which allows the power to pass through the tap, is typically lessthan 0.01 Ohms. Thus total power consumed in the idealized conventionalsystem shown in FIG. 4A is 87.15 watts (85.5+1.95 watts). Cable TV(CATV) operators are extremely interested in reducing power consumptionin their distribution systems. Even a savings of 3 watts, which can save$15 in power costs over 5 years, is considered very favorably.

In 1991, Chiddix and Vaughn proposed a concept of an active tap. Thisproposal was motivated by the difficulties at the time of increasingcable services by just increasing the bandwidth of the distributionplant. The intent of the paper was to encourage manufacturers to helpsolve these problems by building an active tap that would extendservices to a larger number of customers without undue signaldistortion. (In 1991, no CATV distribution equipment was being builtwith GaAs active devices or bipolar transistors with an f_(T) of 6 GHz.Gain stages at the time that were rated above 550 MHz providedadditional bandwidth, but had poor distortion performance.) A smallsegment of a cable system owned by Chiddix's employer was built with abandwidth of 1 GHz to test pay-per-view markets. The system was built inthe traditional way (amplifiers and passive taps). The experiment was amarketing success, but the amplifier distortion performance wasinsufficient, thus making the system impractical.

For many reasons, the active tap proposed by Chiddix and Vaughn were notreduced to practice. First, to achieve suitable performance theequipment power requirements would have increased and the power passingcircuitry did not exist. At the time, it was not possible to makepower-passing circuitry capable of passing in excess of 15 amps withoutsaturating the ferrite coil form, causing modulation of the RF signals.Second, the power consumption of the active tap concept of Chiddix andVaughn, if ever reduced to practice, would have resulted in a systemthat was not cost-effective to operate. For example, if, as described, again stage were used at each subscriber port, a 4-port tap would consumein excess of 32 watts (whereas the device disclosed in the followingdetailed description will provide the same functionality while requiringonly 0.5 watts, providing a $150 savings in powering over five years forevery active tap).

Third, system managers are graded on subscriber minute outages. A 1991cable system could have 100,000 or more subscribers. The signals forthese subscribers would all originate from the head-end and begin byflowing through a single amp. If that amp fails, the network suffers100,000 subscriber minute outages for every minute the system is down.The Chiddix-Vaughn proposal did not reduce the problems associated withamplifier cascades, but added to the system downtime probability byincreasing the number of system power supplies required. Power outagesat supply locations are a major source of system outages.

Fourth, no cable systems have ever been built with 550 MHz, or 1 GHzbandwidth, as suggested by Chiddix and Vaughn. No device was availablethen or is available even today, that could operate at 55 dBmV outputwith 151 analog channels. Furthermore, Chiddix and Vaughn's proposal topower the active tap from one of possible four subscriber's houses addscost, complexity and unreliability to the system. Also, if thesubscriber providing power disconnects, a major reconfiguration of thesystem will be needed.

Fifth, a concern of an active or passive tap system is reverse signallevels. Devices installed in houses have a maximum output of +55 dBmV.The described reverse injection of 30 to 40 dB in the system of Chiddixand Vaughn would not provide enough signal to drive the reverse lasercircuitry at the fiber node. In real applications the directionalcoupler is selected to satisfy the reverse signal requirements.

Sixth, the system of Chiddix and Vaughn is lacks control of signal levelchange due to system ambient temperature changes. The lack of amplitudecontrol and cable versus frequency equalization cause the reach of thesystem to be reduced and could cause unacceptable signal to distortionlevels at the subscriber ports.

Finally, to be cost-effective the system proposed by Chiddix and Vaughnrequired the unit to have a selling price of $100. The cost to build theunit was estimated to be in excess of $120. Manufacturing cost of anoff-premise converter which contained some of the components required,such as microprocessors, hybrids, PIN diode switches, DC power supply,was $235 per subscriber. Because manufacturing costs were estimated tobe more than double what was required to be cost-effective, no deviceswere ever built.

Because the technology of the day did exist to build the devicesuggested by Chiddix and Vaughn, because the overall system waseconomically and operationally inoperative, and because since 1991 theutilization of fiber optics has increased and digital compression of TVchannels have provided a great deal of additional service capacity tothe systems, and improvement in traditional gain stages, including GaAsactive devices has provided a means of building systems with a bandwidthof 870 MHz, the proposal of Chiddix and Vaughn was not reduced topractice.

Thus, what is desired, as discovered by the present inventors, is acapability for distributing coaxial communication signals at greatlyreduced power consumption, and system reliability, where signal levelsand quality are equal to or better than is possible with conventionalamplifier and passive tap systems and where the amplification isprovided at the tap and characterized by low power (less than 1 Watt),low noise figure (less than 3 dB), high bandwidth (typically 20-1.5GHz), and high gain (e.g., input to subscriber output port gain of asmuch as 22 dB).

SUMMARY OF THE INVENTION

The present invention is directed to a low-cost active tap for use incoaxial cable communication distribution systems and characterized bylow system power consumption and low signal distortion, as well asproviding a technically feasible way to increase system bandwidth beyond860 MHz.

The active tap includes a parallel circuit comprising a first powerpassing choke connected to a second power passing choke. In parallel tothe two power passing chokes is a circuit comprising a first capacitor,a directional coupler and second capacitor. A power pick-off tap isplaced between the first and second power passing chokes. 60 Hz power ispassed from the power pick-off tap to the device's DC power supply. Theoutput of the DC power supply is then fed to an amplifier, whichprovides gain for the device. The output of the directional coupler isfed to the combined terminal of a first diplex filter. The output of thehigh pass section of the first diplex filter is fed to the amplifier viaa first attenuator. The output of the amplifier is then fed to a secondhigh pass portion of a second complimentary diplex filter. The output ofthe combined port of the second complimentary diplex filter is then fedto a signal splitter, the split signal coming out of splitter is thenfed to a pair of signal splitters. The output of the second pair ofsplitters and are then fed to four output ports.

While the active tap consumes power, these devices can be used tojudicially replace conventional passive taps within a signaldistribution network to obviate the need for expensive and power hungrytraditional CATV repeater amplifiers, with the net result of loweroverall power consumption and/or a much larger distribution networkbeing supplied by a single power source. In general, factors fordetermining the number of passive and active taps that can be cascadedinclude: A) desired signal level at a node output; B) distance betweentaps; C) density of subscribers; D) size of coaxial cable; and E)efficiency of the directional coupler used in the network (e.g., DC-8,DC-12, DC-16).

Not only do these devices reduce the power required to run the system,they are also producible at much lower costs than conventional CATVrepeater amplifiers (for example, line extenders, trunking amplifiersand bridging amplifiers). Active taps according to the present inventionmay eliminate most bridging amplifiers, trunking amplifiers and lineextenders from coaxial communication networks.

DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic of a conventional passive tap;

FIG. 2 is a block diagram of an idealized signal distribution systemincluding the conventional passive tap of FIG. 1 where the figures ofmerit are signal quality;

FIG. 3 is a block diagram of non-idealized signal distribution systemincluding the conventional passive tap of FIG. 1 where the figures ofmerit are signal quality;

FIG. 4 is a block diagram of an idealized signal distribution systemincluding the conventional passive tap of FIG. 1 where the figure ofmerit is power consumption;

FIG. 5 is a schematic of an active tap according to one embodiment ofthe present invention;

FIG. 6 is a block diagram corresponding to FIG. 4, where the idealizedsignal distribution system includes the active tap of FIG. 5;

FIG. 7 is a block diagram corresponding to FIG. 2, where the idealizedsignal distribution system includes the active tap of FIG. 5;

FIG. 8 is a block diagram corresponding to FIG. 3, where thenon-idealized signal distribution system includes the active tap of FIG.5; and

FIG. 9 is a photograph of connectors used with the device of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 5 shows a block diagram of an embodiment of the present inventionwhich corresponds in function but not in operation with the conventionalpassive tap block diagram of FIG. 1. Here an input value of 12 dBmV ispresented to a parallel circuit comprising a first power passing chokePPC1A connected to a second power passing choke PPC1B. An output tap T1is placed between the first and second power passing chokes (PPC1A andPPC1B). Signal is passed from the output tap T1 to a power supply PS1.The output of the power supply PS1 is then fed to an amplifier AMP1. Inparallel to the two power passing chokes (PPC1A and PPC1B) is a circuit,comprising: a first capacitor C1, a directional coupler DC, and secondcapacitor C2. The output of the directional coupler DC is fed to thecombined port of a first diplex filter D1. The output of the firsthigh-pass filter D1H is fed to the amplifier AMP1 via a first attenuatorA1.

The output of the amplifier is then fed to a second high pass portionD2H of a second diplex filter D2, complimentary to the first diplexfilter D1. The output of the combined terminal of the second high-passfilter is then fed to signal splitter S1, the split signal coming out ofsplitter S1 is then fed to a pair of signal splitters S2A and S2B. Theoutput of the second pair of splitters S2A and S2B are then fed tooutput ports O1, O2, O3, and O4.

Also shown in FIG. 5 is a feedback from the consumer through outputports O1 through O4 to one of a corresponding second signalsplitter/combiner S2A or S2B to signal splitter/combiner S1 back thenthrough the combined terminal of the second complimentary diplex filterthrough the low-pass section of D2L and D1L. In between the first andsecond low-pass filters is an optional attenuator A2 which is used tooptimize signal levels in the reverse system. The output of the combinedterminal of the first low-pass filter D1L is then fed back to the deviceinput via the directional coupler DC.

In the passive tap shown in FIG. 1, signals from the subscriber unitspass backwards through the output ports second splitters/combiners S2Aand S2B, first splitter/combiner S1 and directional coupler DC to theinput. In the active tap shown in FIG. 5, signals from the downstreamconsumer are passed through a respective output port O1 through O4,second splitters/combiners S2A, S2B, first splitter/combiner S1 throughthe low-pass portions (D2L and D1L of diplex filters D1 and D2. Anoptional attenuator A2 is included in between the first and secondlow-pass filters D2L and D1L so as to optimize reverse operating levels.The signal flowing back and out through the low-pass filter D1L is thenfed to the input source through the directional coupler DC. In thepassive tap system of FIG. 1, there is no need for a diplex filterbecause there is no gain stage in a passive tap. When there is no gainstage it is possible to run a reverse signal in the manner similar tothe forward signal.

In one embodiment, the gain stage of the active tap of FIG. 5 has thefollowing characteristics: DC power requirements: 0.5 Watts Max. Noisefigure: 3 dB Max. Bandwidth: Enough to meet current cable systemrequirements typically 20-860 MHz minimum) Gain: Enough gain to provide18 dBmV output at spigot when −4 dBmV is provided at an input byovercoming cable and internal losses such as splitters, diplex filters,etc. RF output capability: 20 dBm min. (P1 dB) Input and Outputimpedance: 50/75 OhmIn order to meet these gain-stage requirements, one embodiment of thepresent invention is developed with monolithic microwave integratedcircuit (MMIC) technology. The MMIC gain stage of the present inventionis characterized by high bandwidth (e.g., DC-2200 MHz), low noise figure(e.g., 3 dB), and low power requirements (e.g., 0.5 W max). One exampledevice that may be used for the gain stage of the present invention isthe AP 112 by RFHIC. While MMIC devices are used to overcome limitationspresented by conventional circuit devices regarding bandwidth, noisefigure, and power consumption, other technologies characterized by highbandwidth, low noise figure, and low power consumption may be used.

In one configuration, the amplifier is configured to provide 31 dB ofgain. In this configuration, an active tap input of 12 dBmV results inoutput of 11 dBmV. As in FIG. 1, the signal level at the directionalcoupler DC is 16 dB lower than the input, thus equal to −4 dBmV at theinput of D1H. After passing through the first high-pass filter D1H andattenuator A1 the value is further reduced to −4.5 dBmV. After passingthrough the amplifier the value is boosted from −4.5 dBmV to 26.5 dBmV.The signal level was reduced upon passing through the second high-passfilter D2H to a value of 26 dBmV thus, the input to splitter S1 is equalto the signal level input to splitter S1 in FIG. 1. However, contrary tothe device of FIG. 1 where the input signal level is 42 dBmV, the inputsignal level of the active tap of FIG. 5 is only 12 dBmV. In thisconfiguration, the active tap of FIG. 5 is estimated to have a powerusage of 0.75 watts, based upon a MMIC drawing about 90 mA at 6 VDC.That is, calculating the DC wattage and then assuming an 80% efficientpower supply results in an AC power consumption of 0.75 watts.

In FIG. 5, directional coupler DC is a DC16 directional coupler (i.e., 1dB insertion loss and 16 dB loss from the coupler input to the coupledport). However, other values of directional couplers (DC12, DC8, etc.are also possible. Also shown in FIGS. 1 and 2 are four output ports O1through O4. However, in other configurations, other numbers of outputports may be arranged. Also, in another embodiment, the active device ofFIG. 5 includes a terminus connected to the output of the second powerpassing choke. This embodiment is used at the end of a distributionline, for example, when the output signal is known to fall below athreshold for adequate amplification.

FIG. 6 corresponds to FIG. 4 where the first four taps are conventionalpassive taps as shown in FIG. 1 and the remaining 13 taps are activetaps (A1-A13) as shown in FIG. 5. (In this configuration, the first fourtaps are conventional passive taps to show the most cost effectivesystem, and since the signal levels are high enough as to not requireamplification. However, in other configurations, all conventionalpassive taps may be replaced by the active tap of FIG. 5.) In FIG. 6,each of the 13 active taps draws approximately 0.75 watts for a totalpower consumption of 9.75 watts. The power consumed by the cable is 10.2milliwatts. Again, the passive taps consume no power. Thus the totalpower consumed with a system shown in FIG. 6 is 9.76 watts. Thus, thepower consumed by the cable television signal distribution system ofFIG. 6 is almost one-tenth of the power consumed by the traditionalsystem shown in FIG. 4.

In alternative configurations, different input voltages and signalfrequencies may also be used. For example, an input of 48 dBmV at 550MHz or 39 dBmV at 55 MHz may be used with a corresponding output signalof 44 or 35 dBmV, respectively. In further configurations, thecomponents shown in FIG. 5 can be replaced or reorganized with othercircuitry so as to provide comparable low power amplification.

FIG. 7, corresponding to FIGS. 2 and 6, illustrates the effect thatactive tap of FIG. 5 has upon signal quality. As in FIG. 2, source I1outputs a signal according the following profile: 54 dBmV at 862 MHz, 48dBmV at 550 MHz, and 39 dBmV at 55 MHz. In addition, the signal outputfrom source I1 has a CTB of −64.0 dB; a CSO of −60.0 dB; and a CNR of51.0 dB. The distortion generated by the active tap amplifier at anoperating level of 26.5 dBmV is as follows: CTB equals −75 dB; CSOequals −60.0 dB; and CNR equals 52.0 dB. The signal quality at allsubscriber output ports is the sum of the source distortions plus thedistortion generated by the active tap gain stage. At the output ofactive tap A13 at the end of the line, CTB is improved over theconventional system of FIG. 2 with a value of −61.8 dB. CSO iseffectively the same as the conventional system of FIG. 2 at a value of−57.0 dB and CNR is 0.8 dB worse, but still exceeds the industry's 48 dBrequirement. (48 dB is a typically required carrier to noise ratio toprevent excess noise or snow from being seen in this display televisionsignal.)

The system of FIG. 6 includes a total of 17 taps whereas the system ofFIG. 2 includes 18 taps. While in the FIGS. 6 and 7 examples it was notpossible to quite reach 18 taps as in the FIG. 2 example, it waspossible to extend the last tap another 29 feet. It is important toagain note, however, that the systems of FIGS. 2 and 6 are grosssimplifications of an actual system and are presented for comparisonpurposes only. In an actual system, footage between taps varies from afew feet to a thousand feet, and usually the line splits multiple timesso that you can run down side streets and such. FIGS. 3 and 8 are morerepresentative of actual cable distribution systems.

FIG. 8 corresponds to FIG. 3, where the line extender LE1 and some ofthe conventional passive taps have been replaced by the active taps ofFIG. 5, resulting in a much larger distribution network being suppliedby source I1. In general, factors for determining the number of passiveand active taps that can be cascaded include: A) desired signal level ata node output; B) distance between taps; C) number of subscribers; D)density of subscribers; E) size of coaxial cable; F) number of multipledwelling units (MDU, e.g., apartments); and G) value and efficiency ofthe directional coupler used (e.g., DC-8, DC-12, DC-16).

With these factors in mind, in FIG. 8 source I1 outputs a signal onto afirst cable C1 of length 271 feet. This signal drops in strength due toline losses and is split by a splitter S1 onto cables C2, C3, and C10.Cable C2 ends after 59 feet at a DC16 active tap A1. Cable C3 extends 84feet to a DC16 active tap A2 which is connected to a DC16 active tap A3via 230 feet of cable C4. Active tap A3 is connected to a DC16 activetap A4 via cable C5. Cable C10 extends 806 feet, equivalent to cable C6and C7 but without line extender LE1, to a DC16 active tap A5. Activetap A5 connects to a DC8 directional coupler DC1 which is connected to aDC16 active tap A6 and to in-line equalizer EQ1. Equalizer EQ1 connectsto cable C8, which extends 259 feet to a conventional DC12 passive tapP7. Passive tap P7 connects to a DC-8 directional coupler DC2 whichconnects to cable C9. Cable C9 extends 277 feet to a DC12 active tap A8.Thus, in FIG. 8, passive taps P1-P6 and P8 have been replaced withactive taps, and LE1 is no longer required.

Furthermore, because the active taps can run on much lower input levelsdue to the internal amplification, additional cable runs and consumerdrops are possible. Also connected to DC2 is a DC16 active tap A9 via268 feet of cable C11. Active tap A9 is connected to equalizer EQ2 via455 feet of cable C12. EQ2 connects to a DC12 active tap A10 whichconnects to a DC8 active tap A11 via 103 feet of cable C13. Active tapA11 connects to a terminating active tap A12 via 85 feet of cable C14.Thus, the configuration of FIG. 8 allows for 16 additional cable drops(via active taps A9-12) over 911 feet of cable (cables C 1′-C 14).

Input and output signal levels (in terms of dBmV) at 862 MHz/750 MHz/55MHz, respectively, are shown in Table T2. TABLE T2 Device Input SignalLevel Output Signal Level I1 —/—/—   50/48/36.5 C1   50/48/36.546.5/44.7/35.6 S1 46.5/44.7/35.6 41.8/40.2/32.1 38.1/36.7/28.6 C238.1/36.7/28.6 37.3/35.6/28.4 A1 37.3/35.6/28.4 18.9/17.6/10.0 C338.1/36.7/28.6   37/35.7/28.4 A2   37/35.7/28.4 18.6/17.6/10.0 C435.9/34.6/28.1 32.9/31.8/27.4 A3 32.9/31.8/27.4 18.0/16.9/12.5 C531.8/30.7/27.1 23.2/22.7/25.3 A4 23.2/22.7/25.3 18.0/17.5/20.0 C1041.8/40.2/32.1 31.3/30.5/29.8 A5 31.3/30.5/29.8 18.0/17.2/16.5 DC130.2/29.4/29.5 28.4/27.6/28.8 22.2/21.4/21.5 A6 22.2/21.4/21.518.0/17.2/18.1 EQ1 28.4/27.6/28.8 28.0/26.2/19.0 C8 28.0/26.2/19.023.8/23.1/17.4 P7 23.8/23.1/17.4 18.0/17.3/11.5 DC2 22.7/22.0/17.120.9/20.2/16.4 14.7/14.0/9.1 C9 14.7/14.0/9.1 11.1/11/8.2 A8 11.1/11/8.218.0/17.8/15.0 C11 20.9/20.2/16.4 16.7/16.5/14.7 A9 16.7/16.5/14.718.0/17.8/16.0 C12 15.6/15.4/14.4  9.7/9.9/13.1 EQ2  9.7/9.9/13.1 9.2/8.5/3.1 A10  9.2/8.5/3.1 18.0/17.2/11.9 C13  8.0/7.3/2.7 6.7/6.0/2.4 A11  6.7/6.0/2.4 18.0/17.3/13.7 C14  4.9/4.2/2.7 3.8/3.2/2.5 A12  3.8/3.2/2.5 18.0/17.4/15.6

One figure of merit relative to the value of the present invention'sactive tap is the installation cost/number of tap outputs. The costs ofall devices used in the conventionally equipped distribution networkwere compared with the costs of all devices used when passive taps arereplaced with active taps of FIG. 5. First, significant cost savingswere accrued by obviating the need for expensive line extenders.Furthermore, the cost of the network was amortizable over a largernumber of customers (e.g., 12 taps with 4 output ports in FIG. 8 vs. 8taps with 4 output ports in FIG. 3), thus providing another figure ofmerit relative to the economic benefit of the device of FIG. 5.

In comparing a large configuration based on distribution networks ofFIGS. 3 and 8, the distribution system with active taps consumed 48%less power than the distribution system with all passive taps. Thus,based on $1/watt/year, the cost to operate the modified system wasestimated to be $280/year less than the conventionally equippeddistribution system. In a second computer model with a more denselypopulated configuration (including a node, eight trunk amplifiers, 73taps, and numerous multiple dwelling units (MDUs), where each MDUrequired a line extender input from the main line, not from a tap). Inthis modeled densely populated configurations, use of the active tap ofFIG. 5 resulted in all 8 trunks being eliminated with all MDUs beingreached at the required input levels. In this second example, the powersavings were estimated to be $516 per year. Not included is the initialcost savings due to requiring 50% fewer power supplies and theirmaintenance.

Another important feature of the present invention is that the activepart of the present invention is not in series with the rest of thedevices downstream. Thus a failure in one unit will result in a maximumof only 4 subscribers losing service. In the case of a bridger or lineextender, however, all subscribers downstream will lose service if thebridger or line extender fails or during normal maintenance. Thus, anetwork using the active tap of FIG. 5 will be characterized by reducedsubscriber outage minutes.

To optimize the system construction cost and provide signal security,the active tap body may be installed with a blanked cover platecontaining no active components. At a later date, when it iseconomically or technically desirable to provide active taps in thesystem the blanked cover plate may be replaced with a new cover platewith the components corresponding to the circuit of FIG. 5 embeddedtherein. FIG. 9 is an illustration of components that would be used tomake the connection in a cover plate that includes embedded activecomponents. Connectors 1001 and 1002 are for the RF connection from thefaceplate to the housing. These two components will match up and slidetogether when the faceplate is inserted into the housing. Connectors1003 and 1004 are configured to provide the AC power used with theactive tap. These connectors may actually be two connectors (power andground). Connectors 1003 and 1004 will be attached to wires that supplypower and ground. Connectors 1003 and 1004 will then be connectedtogether before the cover plate is connected to the housing. The housingcan be environmentally secure, can include RFI protection, can beconfigured for indoor mounting or outdoor strand mounting, and can beconfigured to be cable or AC line powered.

Another benefit of using the active tap of FIG. 5 concerns group delay.In conventional systems there are often a plurality of amplifierscascaded between the fiber node and the customer, where each amplifiertypically includes two diplex filters. Each of these diplex filters ischaracterized by a group delay which causes the signal to be delayed asit passes through the filter. The amount of delay varies with thefrequency of the signal. Because of this frequency-dependent delay, someconventional systems are forced to not use the higher end of thefrequency band (5-42 MHz) in the reverse direction. This reduces theavailable return path bandwidth, which limits the number of customersthat can be supplied with two-way devices such as cable modems andset-top boxes. Because the active tap of FIG. 5 eliminates mostamplifiers and the end-subscriber only sees the active tap's diplexfilter and complimentary filter, group delay in the reverse path isgreatly reduced, thereby preserving reverse-path bandwidth and enablinga broader array of customer services.

Another benefit of using the active tap of FIG. 5 concerns overallbandwidth. In conventional systems amplifiers typically provide up to862 MHz of bandwidth. However, new customer services such as highdefinition television (HDTV) may require more system bandwidth. Becausethe device of FIG. 5 employs monolithic microwave integrated circuit(MMIC) technology, the device can easily support bandwidth expansionbeyond 1 GHz.

In the preceding disclosure, reference has been made to cable televisionsignal distribution. The device of FIG. 5 may also be adapted for use incable audio signal distribution networks as well as cable-based computersignal distribution networks. In addition, the device of FIG. 5 may beadapted for use in fiber-optic television, audio, and computer signaldistribution networks.

The present invention has the additional features of

-   -   Significant reduction in the number of system power supplies        required, and the reduction in cost of maintaining battery and        motor generators due to the decrease in power consumption.    -   A device failure will cause an outage to only a limited number        (typically four) subscribers. For a four subscriber        configuration, an outage would result in four outage minutes per        minute, whereas a conventional system having a failed line        extender would result in wide-scale outages (e.g., a failure of        LE1 in FIG. 2 would result in 52 outage minutes per minute).    -   Maintenance on a device will impact only a limited number of        subscribers (e.g., four subscribers vs. 52 for LE1 in the system        of FIG. 2 described above).    -   Increased reverse bandwidth usability. Digital modulated signals        are sensitive to group delay caused by diplex filters used to        isolate forward signals from reverse signals. The more filters,        the greater the band edge group delay. A conventional system may        have seven isolation filters between the subscriber at the end        of the cascade and the return amplifier. The presented network        is designed to have two high isolation filters and one        complimentary filter which has very little group delay.    -   Advances in medium power MMIC devices make extended system        bandwidth with digital modulated channels to 1 GHz or higher        possible.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than specifically described herein.

1. An active signal tap device, comprising: an input with a minimuminput level of −4 dBmV; at least one signal tap output; and an activecomponent connecting the input to the at least one signal tap output andconfigured to provide an RF output of approximately 18 dBmV with amaximum DC power consumption of no more than 0.5 Watts.
 2. The activesignal tap device of claim 1, wherein said active component comprises: anoise figure of no more than 3 dB.
 3. The active signal tap device ofclaim 1, wherein said active component comprises: a bandwidth of 20MHz-1.5 GHz.
 4. The active signal tap device of claim 1, wherein saidactive component comprises: a gain configured to provide an 18 dBmVoutput signal at said at least one signal tap output.
 5. The activesignal tap device of claim 1, wherein said active component comprises:an input impedance of approximately 75 ohms; and an output impedance ofapproximately 75 ohms.
 6. The active signal tap device of claim 1,wherein said active component comprises: discrete components includingsilicon or GaAs based transistors.
 7. The active signal tap device ofclaim 1, wherein said active component comprises: a MMIC component. 8.The active signal tap device of claim 7, wherein said MMIC componentcomprises: discrete components including silicon or GaAs basedtransistors.
 9. The active signal tap device of claim 1, comprising: afirst AC power passing choke; a second AC power passing choke connectedto the first AC power passing choke; an AC output tap between the firstand second AC power passing chokes; an AC to DC power supply connectedto the AC output tap; an amplifier connected to the DC power supply; acircuit in parallel to the two AC power passing chokes, said circuitcomprising a first capacitor connected to a directional couplerconnected to second capacitor; a first diplex port connected to anoutput of the directional coupler and comprising a first high-passfilter and a first low-pass filter; a first attenuator connecting anoutput of the first high-pass filter to an input to the amplifier; and asecond diplex port connected to an output of the amplifier andcomprising a second high-pass filter and a second low-pass filter. 10.The active signal tap device of claim 9, wherein an output of saidsecond diplex port is connected to said at least one active tap output.11. The active signal tap device of claim 9, further comprising: a firstsignal splitter connected to an output of the second diplex port andhaving a plurality of first signal splitter output ports; a set ofsecond signal splitters connected to the first signal splitter, each ofsaid second signal splitters having a plurality of second signalsplitter output ports; and a plurality of tap ports, each of saidplurality of tap ports connecting a respective second signal splitteroutput port to a respective one of said at least one signal tap output.12. The active signal tap device of claim 11, wherein said plurality offirst signal splitter output ports comprise two first signal splitteroutput ports; and said plurality of second signal splitter output portscomprise two second signal splitter output ports.
 13. The active signaltap device of claim 11, wherein said plurality of first signal splitteroutput ports comprise: two first signal splitter output ports.
 14. Theactive signal tap device of claim 11, wherein said plurality of secondsignal splitter output ports comprise two second signal splitter outputports.
 15. The active signal tap device of claim 9, further comprisingone of: a signal output port connected to an output of said second powerpassing choke; and a terminus connected to an output of said secondpower passing choke.
 16. The active signal tap device of claim 9,further comprising: a feedback circuit connecting the second low-passfilter to the first low-pass filter.
 17. The active signal tap device ofclaim 16, wherein said feedback circuit comprises: a second attenuatorbetween the first and second low-pass filters.
 18. The active signal tapunit of claim 1, further comprising: an environmentally secure housingconfigured to house said active component.
 19. The active signal tapunit of claim 18, wherein the environmentally secure housing comprises:RFI protection.
 20. The active signal tap unit of claim 18, wherein theenvironmentally secure housing comprises one of: a housing configured tobe mounted indoors; and a housing configured to be strand mountedoutdoors.
 21. The active signal tap unit of claim 1, wherein the activecomponent comprises one of: an active component which can be cablepowered; and an active component which can be AC line powered.
 22. Asignal distribution system, comprising: one of a passive tap and a firstactive signal tap; and a second active signal tap connected to the firstactive signal tap, said first and second active signal taps eachincluding an input with a minimum input level of −4 dBmV; at least onesignal tap output; and an active component connecting the input to theat least one signal tap output and configured to provide an RF output ofapproximately 18 dBmV with a maximum DC power consumption of no morethan 0.5 Watts.
 23. The signal distribution system of claim 22, whereinsaid active component comprises: a noise figure of no more than 3 dB.24. The signal distribution system of claim 22, wherein said activecomponent comprises: a bandwidth of 20 MHz-1.5 GHz.
 25. The signaldistribution system of claim 22, wherein said active componentcomprises: a gain configured to provide an 18 dBmV output signal at saidat least one signal tap output.
 26. The signal distribution system ofclaim 22, wherein said active component comprises: an input impedance ofapproximately 75 ohms; and an output impedance of approximately 75 ohms.27. The signal distribution system of claim 22, wherein said activecomponent comprises: discrete components including silicon or GaAs basedtransistors.
 28. The signal distribution system of claim 22, whereinsaid active component comprises: a MMIC component.
 29. The signaldistribution system of claim 22, wherein said MMIC component comprises:discrete components including silicon or GaAs based transistors.
 30. Thesignal distribution system of claim 22, wherein each of said first andsecond active taps comprise: a first AC power passing choke; a second ACpower passing choke connected to the first AC power passing choke; an ACoutput tap between the first and second AC power passing chokes; An ACto DC power supply connected to the AC output tap; an amplifierconnected to the DC power supply; a circuit in parallel to the two ACpower passing chokes, said circuit comprising a first capacitorconnected to a directional coupler connected to second capacitor; afirst diplex filter port connected to an output of the directionalcoupler and comprising a first high-pass filter and a first low-passfilter; a first attenuator connecting an output of the first high-passfilter to an input to the amplifier; and a second diplex filter portconnected to an output of the amplifier and comprising a secondhigh-pass filter and a second low-pass filter.
 31. The signaldistribution system of claim 36, wherein an output of said second diplexfilter port is connected to said at least one active tap output.
 32. Thesignal distribution system of claim 30, wherein at least one of saidfirst and second active taps further comprise: a first signal splitterconnected to an output of the second diplex filter port and having aplurality of first signal splitter output ports; a set of second signalsplitters connected to the first signal splitter, each of said secondsignal splitters having a plurality of second signal splitter outputports; and a plurality of tap ports, each of said plurality of tap portsconnecting a respective second signal splitter output port to arespective one of said at least one signal tap output.
 33. The signaldistribution system of claim 22, further comprising: a signal sourceconnected to said first active tap.
 34. The signal distribution systemof claim 22, wherein one of the first and second active tap comprises:an environmentally secure housing configured to house said correspondingactive component.
 35. The signal distribution system of claim 34,wherein the environmentally secure housing comprises: RFI protection.36. The signal distribution system of claim 34, wherein theenvironmentally secure housing comprises one of: a housing configured tobe mounted indoors; and a housing configured to be strand mountedoutdoors.
 37. The signal distribution system of claim 22, wherein one ofthe first and second active tap comprises one of: an active componentwhich can be cable powered; and an active component which can be AC linepowered.
 38. A method for actively amplifying a signal, comprising:passing an RF signal from an input port to an output port; tapping saidinput RF signal to provide a tapped signal; amplifying said tappedsignal with an active tap configured to consume no more than 0.5 Wattswhile providing a noise figure of no more than 3 dB and a bandwidth of20 MHz-1.5 GHz to provide an amplified tap signal; and passing saidamplified tap signal to a tap output.
 39. The method of claim 38,wherein said step of amplifying with an active tap comprises: amplifyingwith discrete components including silicon or GaAs based transistors.40. The method of claim 38, wherein said step of amplifying with anactive tap comprises: amplifying with a MMIC component.
 41. The methodof claim 40, wherein said step of amplifying with a MMIC componentcomprises: amplifying with discrete components including silicon or GaAsbased transistors.
 42. The method of claim 38, wherein said step ofpassing said amplified tap signal comprises: splitting said amplifiedtap signal.
 43. The method of claim 38, further comprising: passing afeedback signal from said tap output to said input port.
 44. A methodfor distributing an RF signal via cable, comprising: passing an RFsignal through a first active tap; and passing said RF signal through asecond active tap, said second active tap either in series or inparallel with said first active tap, wherein each of said steps ofpassing comprise: tapping an input RF signal to provide a tapped signal;amplifying said tapped signal with an active component consuming no morethan 0.5 Watts and providing a noise figure of no more than 3 dB and abandwidth of 20 MHz-1.5 GHz to provide an amplified tap signal; andoutputting said amplified tap signal to a tap output.
 45. The method ofclaim 44, wherein said step of amplifying comprises: amplifying withdiscrete components including silicon or GaAs based transistors.
 46. Themethod of claim 44, wherein said step of amplifying comprises:amplifying with a MMIC component.
 47. The active signal tap device ofclaim 46, wherein said step of amplifying with a MMIC componentcomprises: amplifying with discrete components including silicon or GaAsbased transistors.
 48. The method of claim 44, wherein said step ofoutputting said amplified tap signal comprises: splitting said amplifiedtap signal.
 49. The method of claim 44, wherein at least one of saidsteps of passing comprise: passing a feedback signal from said tapoutput to said input port.
 50. The method of claim 44, wherein said stepof amplifying said tapped signal with an active tap comprises:amplifying said tapped signal with an active tap housed within anenvironmentally secure housing.
 51. The method of claim 44, wherein saidstep of amplifying said tapped signal with an active tap comprises:amplifying said tapped signal with an active tap housed in a housingprovided with RFI protection.
 52. The method of claim 44, wherein saidstep of amplifying said tapped signal with an active tap comprises oneof: amplifying said tapped signal with an active tap housed in a housingconfigured to be mounted indoors; and amplifying said tapped signal withan active tap housed in a housing configured to be strand mountedoutdoors.
 53. The method of claim 44, wherein said step of amplifyingsaid tapped signal with an active tap comprises one of: amplifying saidtapped signal with an active tap which can be cable powered; andamplifying said tapped signal with an active tap which can be AC linepowered.
 54. A system for actively amplifying a signal, comprising:means for passing an RF signal from an input port to an output port;means for tapping said input RF signal to provide a tapped signal; meansfor amplifying said tapped signal with an active tap configured toconsume no more than 0.5 Watts while providing a noise figure of no morethan 3 dB and a bandwidth of 20 MHz-1.5 GHz to provide an amplified tapsignal; and means for passing said amplified tap signal to a tap output.55. The system of claim 54, wherein said means for amplifying comprises:means for amplifying with discrete components including silicon or GaAsbased transistors.
 56. The system of claim 54, wherein said step ofamplifying comprises: means for amplifying with a MMIC component. 57.The system of claim 56 wherein said means for amplifying with a MMICcomponent comprises: means for discrete components including silicon orGaAs based transistors.
 58. The system of claim 54, wherein said step ofpassing said amplified tap signal comprises: means for splitting saidamplified tap signal.
 59. The system of claim 54, further comprising:means for passing a feedback signal from said tap output to said inputport.
 60. The system of claim 54, wherein said means for amplifying saidtapped signal with an active tap comprises: means for amplifying saidtapped signal with an active tap housed within an environmentally securehousing.
 61. The system of claim 54, wherein said means for amplifyingsaid tapped signal with an active tap comprises: means for amplifyingsaid tapped signal with an active tap housed in a housing provided withRFI protection.
 62. The system of claim 54, wherein said means foramplifying said tapped signal with an active tap comprises one of: meansfor amplifying said tapped signal with an active tap housed in a housingconfigured to be mounted indoors; and means for amplifying said tappedsignal with an active tap housed in a housing configured to be strandmounted outdoors.
 63. The system of claim 54, wherein said means foramplifying said tapped signal with an active tap comprises one of: meansfor amplifying said tapped signal with an active tap which can be cablepowered; and means for amplifying said tapped signal with an active tapwhich can be AC line powered.
 64. A system for distributing an RF signalvia cable, comprising: means for passing an RF signal through a firstactive tap; and means for passing said RF signal through a second activetap, said second active tap either in series or in parallel with saidfirst active tap, wherein each of said means for passing comprise: meansfor tapping an input RF signal to provide a tapped signal; means foramplifying said tapped signal while consuming no more than 0.5 Watts andproviding a noise figure of no more than 3 dB and a bandwidth of 20MHz-1.5 GHz to provide an amplified tap signal; and means for outputtingsaid amplified tap signal to a tap output.
 65. The system of claim 64,wherein said means for amplifying comprises: means for amplifying withdiscrete components including silicon or GaAs based transistors.
 66. Thesystem of claim 64, wherein said step of amplifying comprises: means foramplifying with a MMIC component.
 67. The system of claim 66, whereinsaid means for amplifying with a MMIC component comprises: means foramplifying with discrete components including silicon or GaAs basedtransistors.
 68. The system of claim 64, wherein said step of outputtingsaid amplified tap signal comprises: means for splitting said amplifiedtap signal.
 69. The system of claim 64, wherein at least one of saidsteps of passing comprise: means for passing a feedback signal from saidtap output to said input port.
 70. The system of claim 64, wherein saidmeans for amplifying said tapped signal with an active tap comprises:means for amplifying said tapped signal with an active tap housed withinan environmentally secure housing.
 71. The system of claim 64, whereinsaid means for amplifying said tapped signal with an active tapcomprises: means for amplifying said tapped signal with an active taphoused in a housing provided with RFI protection.
 72. The system ofclaim 64, wherein said means for amplifying said tapped signal with anactive tap comprises one of: means for amplifying said tapped signalwith an active tap housed in a housing configured to be mounted indoors;and means for amplifying said tapped signal with an active tap housed ina housing configured to be strand mounted outdoors.
 73. The system ofclaim 64, wherein said means for amplifying said tapped signal with anactive tap comprises one of: means for amplifying said tapped signalwith an active tap which can be cable powered; and means for amplifyingsaid tapped signal with an active tap which can be AC line powered.